1. Field of the Invention
The present invention relates to a center pillar structure for a vehicle body.
2. Description of the Related Art
Conventionally, using aluminum for structural members of a vehicle body has been considered as a means for reducing the weight of a vehicle. In addition, a frame structure shown in FIG. 5 is one of those designed for passenger vehicles. A center pillar 11 of such a frame structure is displaced at an upper portion thereof inwardly in a transverse direction of the vehicle body so as to correspond to the surface of a side window glass, while at a lower portion the centerpillar 11 is displaced in such a manner as to project outwardly in the transverse direction of the vehicle body so as to accommodate a seat belt retractor.
It is difficult to form the center pillar 11 with an aluminum extruded frame structure, since the configuration of the center pillar 11 is relatively complicated as described above. In addition, it is necessary to cut a portion of the frame after a bending process in order to secure a high accuracy at the joined portions of the frame. The cutting process is complicated and it is hard to form the center pillar as designed. In addition, an aluminum material is first extrusion molded into, for instance, a shape having a quadrangular hollow cross-section. After extrusion molding, the aluminum member is subjected to a bending process as shown in FIG. 6 to achieve the desired configuration. Consequently, a problem arises in which the aluminum member breaks at the time of bending.